Nanostructured fillers and carriers

ABSTRACT

A nanocomposite structure comprising a nanostructured filler or carrier intimately mixed with a matrix, and methods of making such a structure. The nanostructured filler has a domain size sufficiently small to alter an electrical, magnetic, optical, electrochemical, chemical, thermal, biomedical, or tribological property of either filler or composite by at least 20%.

Field of the Invention

[0001] This invention relates to the use of nanoscale powders as acomponent of novel composites and devices. By incorporating powdershaving dimensions less than a characteristic domain size into polymericand other matrices, nanocomposites with unique properties can beproduced.

Background of the Invention

[0002] A very wide variety of pure phase materials such as polymers arenow readily available at low cost. However, low cost pure phasematerials are somewhat limited in the achievable ranges of a number ofproperties, including, for example, electrical conductivity, magneticpermeability, dielectric constant, and thermal conductivity. In order tocircumvent these limitations, it has become common to form composites,in which a matrix is blended with a filler material with desirableproperties. Examples of these types of composites include the carbonblack and ferrite mixed polymers that are used in toners, tires,electrical devices, and magnetic tapes.

[0003] The number of suitable filler materials for composites is large,but still limited. In particular, difficulties in fabrication of suchcomposites often arise due to issues of interface stability between thefiller and the matrix, and because of the difficulty of orienting andhomogenizing filler material in the matrix. Some desirable properties ofthe matrix (e.g., rheology) may also be lost when certain fillers areadded, particularly at the high loads required by many applications. Theavailability of new filler materials, particularly materials with novelproperties, would significantly expand the scope of manufacturablecomposites of this type.

Summary of the Invention

[0004] In one aspect, the invention comprises a nanostructured filler,intimately mixed with a matrix to form a nanostructured composite. Atleast one of the nanostructured filler and the nanostructured compositehas a desired material property which differs by at least 20% from thesame material property for a micron-scale filler or a micron-scalecomposite, respectively. The desired material property is selected fromthe group consisting of refractive index, transparency to light,reflection characteristics, resistivity, permittivity, permeability,coercivity, B-H product, magnetic hysteresis, breakdown voltage, skindepth, curie temperature, dissipation factor, work function, band gap,electromagnetic shielding effectiveness, radiation hardness, chemicalreactivity, thermal conductivity, temperature coefficient of anelectrical property, voltage coefficient of an electrical property,thermal shock resistance, biocompatibility and wear rate.

[0005] The nanostructured filler may comprise one or more elementsselected from the s, p, d, and f groups of the periodic table, or it maycomprise a compound of one or more such elements with one or moresuitable anions, such as aluminum, antimony, boron, bromine, carbon,chlorine, fluorine, germanium, hydrogen, indium, iodine, nickel,nitrogen, oxygen, phosphorus, selenium, silicon, sulfur, or tellurium.The matrix may be a polymer (e.g., poly(methyl methacrylate), poly(vinylalcohol), polycarbonate, polyalkene, or polyaryl), a ceramic (e.g., zincoxide, indium-tin oxide, hafnium carbide, or ferrite), or a metal (e.g.,copper, tin, zinc, or iron). Loadings of the nanofiller may be as highas 95%, although loadings of 80% or less are preferred. The inventionalso comprises devices which incorporate the nanofiller (e.g.,electrical, magnetic, optical, biomedical, and electrochemical devices).

[0006] Another aspect of the invention comprises a method of producing acomposite, comprising blending a nanoscale filler with a matrix to forma nanostructured composite. Either the nanostructured filler or thecomposite itself differs substantially in a desired material propertyfrom a micron-scale filler or composite, respectively. The desiredmaterial property is selected from the group consisting of refractiveindex, transparency to light, reflection characteristics, resistivity,permittivity, permeability, coercivity, B-H product, magnetichysteresis, breakdown voltage, skin depth, curie temperature,dissipation factor, work function, band gap, electromagnetic shieldingeffectiveness, radiation hardness, chemical reactivity, thermalconductivity, temperature coefficient of an electrical property, voltagecoefficient of an electrical property, thermal shock resistance,biocompatibility, and wear rate. The loading of the filler does notexceed 95 volume percent, and loadings of 80 volume percent or less arepreferred.

[0007] The composite may be formed by mixing a precursor of the matrixmaterial with the nanofiller, and then processing the precursor to forma desired matrix material. For example, the nanofiller may be mixed witha monomer, which is then polymerized to form a polymer matrix composite.In another embodiment, the nanofiller may be mixed with a matrix powdercomposition and compacted to form a solid composite. In yet anotherembodiment, the matrix composition may be dissolved in a solvent andmixed with the nanofiller, and then the solvent may be removed to form asolid composite. In still another embodiment, the matrix may be a liquidor have liquid like properties.

[0008] Many nanofiller compositions are encompassed within the scope ofthe invention, including nanofillers comprising one or more elementsselected from the group consisting of actinium, aluminum, arsenic,barium, beryllium, bismuth, cadmium, calcium, cerium, cesium, cobalt,copper, dysprosium, erbium, europium, gadolinium, gallium, gold,hafnium, hydrogen, indium, iridium, iron, lanthanum, lithium, magnesium,manganese, mendelevium, mercury, molybdenum, neodymium, neptunium,nickel, niobium, osmium, palladium, platinum, potassium, praseodymium,promethium, protactinium, rhenium, rubidium, scandium, silver, sodium,strontium, tantalum, terbium, thallium, thorium, tin, titanium,tungsten, vanadium, ytterbium, yttrium, zinc, and zirconium.

[0009] “Domain size,” as that term is used herein, refers to the minimumdimension of a particular material morphology. In the case of powders,the domain size is the grain size. In the case of whiskers and fibers,the domain size is the diameter. In the case of plates and films, thedomain size is the thickness.

[0010] As used herein, a “nanostructured” powder is one having a domainsize of less than 100 nm, or alternatively, having a domain sizesufficiently small that a selected material property is substantiallydifferent from that of a micron-scale powder, due to size confinementeffects (e.g., the property may differ by 20% or more from the analogousproperty of the micron-scale material). Nanostructured powders oftenadvantageously have sizes as small as 50 nm, 30 run, or even smaller.Nanostructured powders may also be referred to as “nanopowders,” or“nanofillers.” A nanostructured composite is a composite comprising ananostructured phase dispersed in a matrix.

[0011] As it is used herein, the term “agglomerated” describes a powderin which at least some individual particles of the powder adhere toneighboring particles, primarily by electrostatic forces, and“aggregated” describes a powder in which at least some individualparticles are chemically bonded to neighboring particles.

[0012] As it is used herein, the term “device” includes mechanical,electrical, electronic, biomedical, and other apparatuses and structureswhich may be manufactured for a wide variety of purposes.

Brief Description of the Drawing

[0013] The invention is described with reference to the several figuresof the drawing, in which,

[0014]FIG. 1 is a diagram of a nanostructured filler coated with apolymer;

[0015]FIG. 2 portrays an X-ray diffraction (XRD) spectrum for thestoichiometric indium tin oxide powder of Example 1;

[0016]FIG. 3 is a scanning electron microscope (SEM) micrograph of thestoichiometric indium tin oxide powder of Example 1; and

[0017]FIG. 4 is a diagram of the nanostructured varistor of Example 5.

Detailed Description

[0018] Prior art filler materials for polymeric composites are usuallypowders with an average dimension in the range of 10-100 μm. Thus, eachfiller particle typically has on the order of 10¹⁵-10¹⁸ atoms. Incontrast, the typical polymer chain has on the order of 10³-10⁹atoms.While the art of precision manufacturing of polymers at molecular levelsis well-developed, the knowledge of precision manufacturing of fillermaterials at molecular levels has remained largely unexplored.

[0019] The number of atoms in the filler particles of the invention(hereinafter called “nanostructured filler” or “nanofiller”) is on theorder of or significantly less than the number of atoms in the polymermolecules, e.g., 10²-10¹⁰ . Thus, the filler particles are comparable insize or smaller than the polymer molecules, and therefore can bedispersed with orders of magnitude higher number density. Further, thefillers may have a dimension less than or equal to the critical domainsizes that determine the characteristic properties of the bulkcomposition; thus, the fillers may have significantly different physicalproperties from larger particles of the same composition. This in turnmay yield markedly different properties in composites using nanofillersas compared to the typical properties of conventional polymercomposites.

[0020] These nanostructured filler materials may also have utility inthe manufacture of other types of composites, such as ceramic- ormetal-matrix composites. Again, the changes in the physical propertiesof the filler particles due to their increased surface area andconstrained domain sizes can yield changes in the achievable propertiesof composites.

[0021] The nanofillers of the invention can be inorganic, organic, ormetallic, and may be in the form of powders, whiskers, fibers, plates orfilms. The fillers represent an additive to the overall compositecomposition, and may be used at loadings of up to 95% by volume. Thefillers may have connectivity in 0, 1, 2, or 3 dimensions. Fillers maybe produced by a variety of methods, such as those described in U.S.Pat. Nos. 5,486,675; 5,447,708; 5,407,458; 5,219,804; 5,194,128; and5,064,464. Particularly preferred methods of making nanostructuredfillers are described in U.S. Patent Application Nos. 09/046,465, byBickmore, et al., filed Mar. 23, 1998, and 08/706,819, by Pirzada, etal., filed Sep. 3, 1996, both of which are incorporated herein byreference.

[0022] A wide variety of nanofiller compositions are possible. Someexemplary compositions include metals (e.g., Cu, Ag, Ni, Fe, Al, Pd, andTi), oxide ceramics (e.g., TiO₂, TiO_(2-X), BaFe₂O₄, dielectriccompositions, ferrites, and manganites), carbide ceramics (e.g., SiC,BC, TiC, WC, WC_(1-x)), nitride ceramics (e.g., Si₃N₄, TiN, VN, AlN, andMo₂N), hydroxides (e.g., aluminum hydroxide, calcium hydroxide, andbarium hydroxide), borides (e.g., AlB₂ and TiB₂), phosphides (e.g., NiPand VP), sulfides (e.g., molybdenum sulfide, titanium sulfide, andtungsten sulfide), suicides (e.g., MoSi₂), chalcogenides (e.g., Bi₂Te₃,Bi₂Se₃), and combinations of these.

[0023] The fillers are intimately mixed with a matrix material, which ispreferably polymeric, but may also be ceramic, metallic, or acombination of the above. The matrix may be chosen for properties suchas ease of processability, low cost, environmental benignity, commercialavailability, and compatibility with the desired filler. The fillers arepreferably mixed homogeneously into the matrix, but may also be mixedheterogeneously if desired, for example to obtain a composite having agradient of some property. Mixing techniques for incorporating powdersinto fluids and for mixing different powders are well known in the art,and include mechanical, thermal, electrical, magnetic, and chemicalmomentum transfer techniques, as well as combinations of the above.

[0024] The viscosity, surface tension, and density of a liquid matrixmaterial can be varied for mixing purposes, the preferred values beingthose that favor ease of mixing and that reduce energy needed to mixwithout introducing any undesirable contamination. One method of mixingis to dissolve the matrix in a solvent which does not adversely affectthe properties of the matrix or the filler and which can be easilyremoved and recovered. Another method is to melt the matrix, incorporatethe filler, and cool the mixture to yield a solid composite with thedesired properties. Yet another method is to synthesize the matrixin-situ with the filler present. For example, the nanofiller can bemixed with a liquid monomer, which can then be polymerized to form thecomposite. In this method, the filler may be used as a catalyst orco-catalyst for polymerization. The mixing may also be accomplished inthe solid state, for example by mixing a powdered matrix compositionwith the filler, and then compacting the mixture to form a solidcomposite.

[0025] Mixing can be assisted using various secondary species such asdispersants, binders, modifiers, detergents, and additives. Secondaryspecies may also be added to enhance one or more of the properties ofthe filler-matrix composite.

[0026] Mixing can also be assisted by pre-coating the nanofiller with athin layer of the matrix composition or with a phase that is compatiblewith the matrix composition. Such a coated nanoparticle is illustratedin FIG. 1, which shows a spherical nanoparticle 6 and a coating 8. Inone embodiment, when embedding nanofillers in a polymer matrix, it maybe desirable to coat the filler particles with a related monomer. Whenmixing nanofillers into a ceramic matrix, pre-coating can be done byforming a ceramic layer around the nanoscale filler particle during orafter the synthesis of the nanoscale filler, by methods such as partialoxidation, nitridation, carborization, or boronation. In these methods,the nanostructured filler is exposed to a small concentration of aprecursor that reacts with the surface of the filler to form a ceramiccoating. For example, a particle may be exposed to oxygen in order tocreate an oxide coating, to ammonia in order to create a nitridecoating, to borane to create a boride coating, or to methane to create acarbide coating. It is important that the amount of precursor be small,to prevent thermal runaway and consequent conversion of thenanostructured filler into a ceramic particle.

[0027] In case of polymer matrix, the filler can be coated with apolymer or a monomer by numerous methods, for example, surface coatingin-situ, spray drying a dispersion of filler and polymer solution,co-polymerization on the filler surface, and melt spinning followed bymilling. A preferred method is surface coating in-situ. In this process,the filler is first suspended in demineralized water (or anothersolvent) and the suspension's pH is measured. The pH is then adjustedand stabilized with small addition of acid (e.g., acetic acid or dilutenitric acid) or base (e.g., ammonium hydroxide or dilute sodiumhydroxide). The pH adjustment produces a charged state on the surface ofthe filler. Once a desired pH has been achieved, a coating material (forexample, a polymer or other appropriate precursor) with opposite chargeis introduced into the solvent. This step results in coupling of thecoating material around the nanoscale filler and formation of a coatinglayer around the nanoscale filler. Once the layer has formed, the filleris removed from the solvent by drying, filtration, centrifugation, orany other method appropriate for solid-liquid separation. This techniqueof coating a filler with another material using surface charge can beused for a variety of organic and inorganic compositions.

[0028] When a solvent is used to apply a coating as in the in-situsurface coating method described above, the matrix may also be dissolvedin the solvent before or during coating, and the final composite formedby removing the solvent.

[0029] A very wide range of material properties can be engineered by thepractice of the invention. For example, electrical, magnetic, optical,electrochernical, chemical, thermal, biomedical, and tribologicalproperties can be varied over a wider range than is possible using priorart micron-scale composites.

[0030] Nanostructured fillers can be used to lower or raise theeffective resistivity, effective permittivity, and effectivepermeability of a polymer or ceramic matrix. While these effects arepresent at lower loadings, they are expected to be most pronounced forfiller loadings at or above the percolation limit of the filler in thematrix (i.e., at loadings sufficiently high that electrical continuityexists between the filler particles). Other electrical properties whichmay be engineered include breakdown voltage, skin depth, curietemperature, temperature coefficient of electrical property, voltagecoefficient of electrical property, dissipation factor, work function,band gap, electromagnetic shielding effectiveness and degree ofradiation hardness. Nanostructured fillers can also be used to engineermagnetic properties such as the coercivity, B-H product, hysteresis, andshape of the B-H curve of a matrix.

[0031] An important characteristic of optical material is its refractiveindex and its transmission and reflective characteristics.Nanostructured fillers may be used to produce composites with refractiveindex engineered for a particular application. Gradient lenses may beproduced using nanostructured materials. Gradient lenses produced fromnanostructured composites may reduce or eliminate the need for polishinglenses. The use of nanostructured fillers may also help filter specificwavelengths. Furthermore, a key advantage of nanostructured fillers inoptical applications is expected to be their enhanced transparencybecause the domain size of nanostructured fillers ranges from about thesame as to more than an order of magnitude less than visible wavelengthsof light.

[0032] The high surface area and small grain size of nanofilledcomposites make them excellent candidates for chemical andelectrochemical applications. When used to form electrodes forelectrochemical devices, these materials are expected to significantlyimprove performance, for example by increasing power density inbatteries and reducing minimum operating temperatures for sensors. (Anexample of the latter effect can be found in copending and commonlyassigned U.S. application Ser. No. 08/739,257, “Nanostructured IonConducting Solid Electrolytes,” by Yadav, et al.). Nanostructuredfillers are also expected to modify the chemical properties ofcomposites. These fillers are catalytically more active, and providemore interface area for interacting with diffusive species. Such fillersmay, for example, modify chemical stability and mobility of diffusinggases. Furthermore, nanostructured fillers may enhance the chemicalproperties of propellants and fuels.

[0033] Is Many nanostructured fillers have a domain size comparable tothe typical mean free path of phonons at moderate temperatures. It isthus anticipated that these fillers may have dramatic effects on thethermal conductivity and thermal shock resistance of matrices into whichthey are incorporated.

[0034] Nanostructured fillers—in coated and uncoated form—and nanofilledcomposites are also expected to have significant value in biomedicalapplications for both humans and animals. For example, the small size ofnanostructured fillers may make them readily transportable through poresand capillaries. This suggests that the fillers may be of use indeveloping novel time-release drugs and methods of administration anddelivery of drugs, markers, and medical materials. A polymer coating canbe utilized either to make water-insoluble fillers into a form that iswater soluble, or to make water-soluble fillers into a form that iswater insoluble. A polymer coating on the filler may also be utilized asa means to time drug-release from a nanoparticle. A polymer coating mayfurther be used to enable selective filtering, transfer, capture, andremoval of species and molecules from blood into the nanoparticle.

[0035] A nanoparticulate filler for biomedical operations might be acarrier or support for a drug of interest, participate in the drug'sfunctioning, or might even be the drug itself. Possible administrationroutes include oral, topical, and injection routes. Nanoparticulates andnanocomposites may also have utility as markers or as carriers formarkers. Their unique properties, including high mobility and unusualphysical properties, make them particularly well-adapted for such tasks.

[0036] In some examples of biomedical functions, magnetic nanoparticlessuch as ferrites may be utilized to carry drugs to a region of interest,where the particles may then be concentrated using a magnetic field.Photocatalytic nanoparticles can be utilized to carry drugs to region ofinterest and then photoactivated. Thermally sensitive nanoparticles cansimilarly be utilized to transport drugs or markers or species ofinterest and then thermally activated in the region of interest.Radioactive nanoparticulate fillers may have utility for chemotherapy.Nanoparticles suitably doped with genetic and culture material may beutilized in similar way to deliver therapy in target areas.Nanocomposites may be used to assist in concentrating the particle andthen providing the therapeutic action. To illustrate, magnetic andphotocatalytic nanoparticles may be formed into a composite,administered to a patient, concentrated in area of interest usingmagnetic field, and finally activated using photons in the concentratedarea. As markers, nanoparficulate fillers-coated or uncoated-may be usedfor diagnosis of medical conditions. For example, fillers may beconcentrated in a region of the body where they may be viewed bymagnetic resonance imaging or other techniques. In all of theseapplications, the possibility exists that nanoparticulates can bereleased into the body in a controlled fashion over a long time period,by implanting a nanocomposite material having a bioabsorbable matrix,which slowly dissolves in the body and releases its embedded filler.

[0037] As implants, nanostructured fillers and composites are expectedto lower wear rate and thereby enhance patient acceptance of surgicalprocedures. Nanostructured fillers may also be more desirable thanmicron-scale fillers, because the possibility exists that their domainsize may be reduced to low enough levels that they can easily be removedby normal kidney action without the development of stones or otheradverse side effects. While nanoparticulates may be removed naturallythrough kidney and other organs, they may also be filtered or removedexternally through membranes or otherwise removed directly from blood ortissue. Carrier nanoparticulates may be reactivated externally throughmembranes and reused; for example, nutrient carriers may be removed fromthe bloodstream, reloaded with more nutrients, and returned to carry thenutrients to tissue. The reverse process may also be feasible, whereincarriers accumulate waste products in the body, which are removedexternally, returning the carriers to the bloodstream to accumulate morewaste products.

EXAMPLES Example 1

[0038] Indium Tin Oxide fillers in PMMA

[0039] A stoichiometric (90 wt % In₂O₃ in SnO₂) indium tin oxide (ITO)nanopowder was produced using the methods of copending patentapplication 09/046,465. 50 g of indium shot was placed in 300 ml ofglacial acetic acid and 10 ml of nitric acid. The combination, in a 1000ml Erlenmeyer flask, was heated to reflux while stirring for 24 hours.At this point, 50 ml of HNO₃ was added, and the mixture was heated andstirred overnight. The solution so produced was clear, with all of theindium metal dissolved into the solution, and had a total final volumeof 318 ml. An equal volume (318 mL) of 1 -octanol was added to thesolution along with 600 mL ethyl alcohol in a 1000 mL HDPE bottle, andthe resulting mixture was vigorously shaken. 11.25 ml of tetrabutyltinwas then stirred into the solution to produce a clear indium/tinemulsion. When the resulting emulsion was burned in air, it produced abrilliant violet flame. A yellow nanopowder residue was collected fromthe flamed emulsion. The nanopowder surface area was 13.5 m²/gm, andx-ray diffractometer mean grain size was 60 nm.

[0040]FIG. 2 shows the measured X-ray diffraction (XRD) spectrum for thepowder, and FIG. 3 shows a scanning electron microscope (SEM) image ofthe powder. These data show that the powder was of nanometer scale.

[0041] The nanostructured powder was then mixed with poly(methylmethacrylate) (PMMA) in a ratio of 20 vol % powder to 80 vol % PMMA. Thepowder and the polymer were mixed using a mortar and pestle, and thenseparated into three parts, each of which was pressed into a pellet. Thepellets were pressed by using a Carver hydraulic press, pressing themixture into a ¼ inch diameter die using a 1500 pound load for oneminute.

[0042] After removal from the die, the physical dimensions of thepellets were measured, and the pellets were electroded with silverscreen printing paste (Electro Sciences Laboratory 9912-F).

[0043] Pellet resistances were measured at 1 volt using a Megohmmeter/IRtester 1865 from QuadTech with a QuadTech component test fixture. Thevolume resistivity was calculated for each pellet using the standardrelation, $\begin{matrix}{\rho = {R\left( \frac{A}{t} \right)}} & (1)\end{matrix}$

[0044] where ρrepresents volume resistivity in ohm-cm, R represents themeasured resistance in ohms, A represents the area of the electrodedsurface of the pellet in cm², and t represents the thickness of thepellet in cm. The average volume resistivity of the stoichiometric ITOcomposite pellets was found to be 1.75×10⁴ ohm-cm.

[0045] Another quantity of ITO nanopowder was produced as describedabove, and was reduced by passing 2 SCFM of forming gas (5% hydrogen innitrogen) over the powder while ramping temperature from 25° C. to 250°C. at 5 ° C./min. The powder was held at 250° C. for 3 hours, and thencooled back to room temperature. The XRD spectrum of the resultingpowder indicated that the stoichiometry of the reduced powder wasIn₁₈SnO_(29-x), with x greater than 0 and less than 29.

[0046] The reduced ITO nanopowder was combined with PMMA in a 20:80volume ratio and formed into pellets as described above. The pelletswere electroded as described, and their resistivity was measured. Theaverage resistivity for the reduced ITO composite pellets was found tobe 1.09×10⁴ ohm-cm.

[0047] For comparison, micron scale ITO was purchased from Alfa Aesar(catalog number 36348), and was formed into pellets with PMMA andelectroded as described above. Again, the volume fraction of ITO was20%. The average measured resistivity of the micron scale ITO compositepellets was found to be 8.26×10⁸ ohm-cm, representing a difference ofmore than four orders of magnitude from the nanoscale composite pellets.It was thus established that composites incorporating nanoscale fillerscan have unique properties not achievable by prior art techniques.

Example 2

[0048] Hafnium Carbide fillers in PMMA

[0049] Nanoscale hafnium carbide fillers were prepared as described incopending U.S. patent applications Nos. 08/706,819 and 08/707,341. Thenanopowder surface area was 53.5 m²/gm, and mean grain size was 16 nm.Micron scale hafnium carbide powder was purchased from Cerac (catalognumber H-1004) for comparison.

[0050] Composite pellets were produced as described in Example 1, bymixing filler and polymer with a mortar and pestle and pressing in ahydraulic press. Pellets were produced containing either nanoscale ormicron scale powder at three loadings: 20 vol % powder, 50 vol % powder,and 80 vol % powder. The pellets were electroded as described above, andtheir resistivities were measured. (Because of the high resistances atthe 20% loading, these pellets'resistivities were measured at 100V. Theother pellets were measured at IV, as described in Example 1).

[0051] Results of these resistivity measurements are summarized inTable 1. As can be seen, the resistivity of the pellets differedsubstantially between the nanoscale and micron scale powders. Thecomposites incorporating nanoscale powder had a somewhat decreasedresistivity compared to the micron scale powder at 20% loading, but hada dramatically increased resistivity compared to the micron scale powderat 50% and 80% loading. TABLE 1 Volume % Resistivity of nanoscaleResistivity of micron scale filler powder composite (ohm-cm) powdercomposite (ohm-cm) 20   5.54 × 10¹²   7.33 × 10¹³ 50 7.54 × 10⁹ 2.13 ×10⁴ 80 3.44 × 10⁹ 1.14 × 10⁴

Example 3

[0052] Copper fillers in PMMA and PVA

[0053] Nanoscale copper powders were produced as described in U.S.patent applications Nos. 08/06,819 and 08/707,341. The nanopowdersurface area was 28.1 m2/gm, and mean grain size was 22 nm. Micron scalecopper powder was purchased from Aldrich (catalog number 32645-3) forcomparison.

[0054] The nanoscale and micron scale copper powders were each mixed ata loading of 20 vol % copper to 80 vol % PMMA and formed into pellets asdescribed above. In addition, pellets having a loading of 15 vol %copper in poly(vinyl alcohol) (PVA) were produced by the same method.The pellets were electroded and resistivities measured at 1 volt asdescribed in Example 1. Results are shown in Table 2. TABLE 2 Volume %Volume Resistivity Additive Polymer filler (ohm-cm) nanoscale copperPMMA 20 5.68 × 10¹⁰ nanoscale copper PVA 15 4.59 × 10⁵  micron scalecopper PMMA 20 4.19 × 10¹²

[0055] It can be seen from Table 2 that the resistivity of the nanoscalecopper powder/PMMA composite was substantially reduced compared to themicron scale copper powder/PMMA composite at the same loading, and thatthe resistivity of the nanoscale copper powder/PVA composite was lowerstill by five orders of magnitude.

Example 4

[0056] Preparation of Polymer-coated Nanostructured Filler

[0057] The stoichiometric (90 wt % In_(2O) _(3 in SnO) ₂) indium tinoxide (ITO) nanopowder of Example 1 was coated with a polymer asfollows.

[0058] 200 milligrams of ITO nanopowders with specific surface area of53 m²/gm were added to 200 ml of demineralized water. The pH of thesuspension was adjusted to 8.45 using ammonium hydroxide. In anothercontainer, 200 milligrams of poly(methyl methacrylate) (PMMA) wasdissolved in 200 ml of ethanol. The PMMA solution was warmed to 100° C.while being stirred. The ITO suspension was added to the PMMA solutionand the stirring and temperature of 100° C. was maintained till thesolution reduced to a volume of 200 ml. The solution was then cooled toroom temperature to a very homogenous solution with very lightclear-milky color. The optical clarity confirmed that the powders arestill nanostructured. The powder was dried in oven at 120° C. and itsweight was measured to be 400 milligrams. The increase in weight,uniformity of morphology and the optical clarity confirmed that thenanopowders were coated with PMMA polymer.

[0059] The electrochemical properties of polymer coated nanopowders weredifferent than the as-produced nanopowders. The as-produced nanopowderwhen suspended in demineralized water yielded a pH of 3.4, while thepolymer coated nanopowders had a pH of 7.51.

Example 5

[0060] Preparation of Electrical Device Using Nanostructured Fillers

[0061] A complex oxide nanoscale filler having the following compositionwas prepared: Bi₂O₃ (48.8 wt %), NiO (24.4 wt %), CoO (12.2 w %), Cr₂O₃(2.4 wt %), MnO(12.2 wt %), and A1₂O₃ (<0.02 wt %). The complex oxidefiller was prepared from the corresponding nitrates of the same cation.The nitrates of each constituent were added to 200 mL of deionized waterwhile constantly stirring. Hydroxides were precipitated with theaddition of 50 drops of 28-30% NH₄OH. The solution was filtered in alarge buchner funnel and washed with deionized water and then with ethylalcohol. The powder was dried in an oven at 80° C. for 30 minutes. Thedried powder was ground using a mortar and pestle. A heat treatmentschedule consisting of a 15 ° C./min ramp to 350° C. with a 30 minutedwell was used to calcine the ground powder.

[0062] The nanofiller was then incorporated at a loading of 4% into azinc oxide ceramic matrix. The composite was prepared by mechanicallymixing the doped oxide nanofiller powder with zinc oxide powder,incorporating the mixture into a slurry, and screen printing the slurry(further described below). For comparison, devices were made using botha nanoscale matrix powder produced by the methods of copending andcommonly assigned U.S. application Ser. No. 08/706,819, and using amicron scale matrix powder purchased from Chemcorp. The fillers and thematrix powders were mixed mechanically using a mortar and pestle.

[0063] Using the filler-added micron scale powder, a paste was preparedby mixing 4.0 g of powder with 2.1 g of a commercial screen printingvehicle purchased from Electro Science Laboratories (ESL vehicle 400).The doped nanoscale powder paste was made using 3.5 g powder and 3.0 gESL vehicle 400. Each paste was mixed using a glass stir rod.Silver-palladium was used as a conducting electrode material. A screenwith a rectangular array pattern was used to print each paste on analumina substrate. First a layer of silver-palladium powder (the lowerelectrode) was screen printed on the substrate and dried on a hot plate.Then the ceramic filled powder was deposited, also by screen printing.Four print-dry cycles were used to minimize the possibility of pinholedefects in the varistor. Finally, the upper electrode was deposited.

[0064] The electrode/composite/electrode varistor was formed as threediagonally offset overlapping squares, as illustrated in FIG. 4. Theeffective nanostructured-filler based composite area in the device dueto the offset of the electrodes was 0.036 in² (0.2315 cm²). The greenthick films were co-fired at 900° C. for 60 minutes. The screen printedspecimen is shown in FIG. 4, where light squares 10 represent thesilver-palladium electrodes, and dark square 12 represents the compositelayer.

[0065] Silver leads were attached to the electrodes using silver epoxy.The epoxy was cured by heating at a 50 ° C./min ramp rate to 600° C. andthen cooling to room temperature at a rate of 50 ° C./min. TheTestPoint™ computer software, in conjunction with a Keithley® currentsource, was used to obtain a current-voltage curve for each of thevaristors.

[0066] The electrode/micron scale matrix composite/electrode basedvaristor device had a total thickness of 29-33 microns and a compositelayer thickness of 19 microns. The electrode/nanoscale matrixcomposite/electrode based varistor device had a total thickness of 28-29microns and a composite layer thickness of 16 microns. Examination ofcurrent-voltage response curves for both varistors showed that thenanostructured matrix varistor had an inflection voltage of about 2volts, while the inflection voltage of the micron scale matrix varistorhad an inflection voltage of about 36 volts. Fitting the current-voltageresponse curves to the standard varistor power-law equation

I=nV^(α)  (2)

[0067] yielded values of voltage parameter αof 2.4 for the micron-scalematrix device, and 37.7 for the nanoscale matrix device. Thus, thenonlinearity of the device was shown to increase dramatically when thenanoscale matrix powder was employed.

Example 6

[0068] Thermal battery electrode using a nanostructured filler

[0069] Thermal batteries are primary batteries ideally suited formilitary ordinance, projectiles, mines, decoys, torpedoes, and spaceexploration systems, where they are used as highly reliable energysources with high power density and extremely long shelf life. Thermalbatteries have previously been manufactured using techniques that placeinherent limits on the minimum thickness obtainable while ensuringadequate mechanical strength. This in turn has slowed miniaturizationefforts and has limited achievable power densities, activationcharacteristics, safety, and other important performancecharacteristics. Nanocomposites help overcome this problem, as shown inthe following example.

[0070] Three grams of raw FeS₂ powder was mixed and milled with a groupof hard steel balls in a high energy ball mill for 30 hours. The grainsize of produced powder was 25 nm. BET analysis showed the surface areaof the nanopowder to be 6.61 m²/gm. The TEM images confirmed that theball milled FeS₂ powder consists of the fine particles with the roundshape, similar thickness and homogenous size. The cathode comprised FeS₂nanopowders (68%), eutectic LiCl-KCl (30%) and SiO₂ (2%) (from AldrichChemical with 99% purity). The eutectic salts enhanced the diffusion ofLi ions and acted as a binder. Adding silicon oxide particles wasexpected to immobilize the LiCl-KCl salt during melting. For comparison,the cathode pellets were prepared from nanostructured and micron scaleFeS₂ powders separately.

[0071] To improve electrochemical efficiencies and increase the meltingpoint of anode, we chose micron scale Li 44%-Si 56% alloy with 99.5%purity (acquired from Cyprus Foote Mineral) as the anode material inthis work. A eutectic salt, LiCl 45%-KCl 55% (from Aldrich Chemical with99% purity), was selected as electrolyte. The salt was dried at 90° C.and fused at 500° C. To strengthen the pellets and prevent flowing outof electrolyte when it melted, 35% MgO (Aldrich Chemical, 99% purity)powder was added and mixed homogeneously with the eutectic salt powder.

[0072] The pellets of anode electrodes were prepared by a cold pressprocess. A hard steel die with a 20 mm internal diameter was used tomake the thin disk pellets. 0.314 grams of Li 44%-Si 56% alloy powder(with 76-422 mesh particle size) was pressed under 6000 psi staticpressure to form a pellet. The thickness and density of the pellets soobtained was determined to be 0.84 mm and 1.25 g/cm², respectively.Electrolyte pellets were produced using 0.55 grams of blendedelectrolyte powder under 4000 psi static pressure. The thickness anddensity of the pellets obtained were 0.84 mm and 2.08 g/cm²respectively. The cathode pellet was prepared using 0.91 grams of mixedmicron scale FeS₂—LiCl—KCl—SiO₂ powder pressed under 4000 psi staticpressure. The thickness and density of the pellets obtained were 0.86 mmand 3.37 g/cm², respectively.

[0073] A computerized SOLARTRONO® 1287 electrochemical interface and a1260 Gain/Phase Analyzer were employed to provide constant current andto monitor variation in potential between anode and cathode of cellsduring the discharging. The cutoff potential of discharge was set at 0.8volt. The thermal battery with the nanocomposite cathode provided 1Aconstant current for 246 seconds, until the potential fell to 0.8 volt.It was observed that the power density of the nanostructured single cellthermal battery was 100% higher than that achievable with micron sizedmaterials. Thus, nanoscale fillers can help enhance the electrochemicalperformance of such a device.

Example 7

[0074] A magnetic device using nanostructured ferrite fillers

[0075] Ferrite inductors were prepared using nanostructured andmicron-scale powders as follows. One-tenth of a mole (27.3 grams) ofiron chloride hexahydrate (FeCl₃-6H₂0) was dissolved in 500 ml ofdistilled water along with 0.025 moles (3.24 grams) of nickel chloride(NiCl₂) and 0.025 moles (3.41 grams) of zinc chloride (ZnCl₂). Inanother large beaker, 25 grams of NaOH was dissolved in 500 ml ofdistilled water. While stirring the NaOH solution rapidly, the metalchloride solution was slowly added, forming a precipitateinstantaneously. After 1 minute of stirring, the precipitate solutionwas vacuum filtered while frequently rinsing with distilled water. Afterthe precipitate had dried enough to cake and crack, it was transferredto a glass dish and allowed to dry for 1 hour in an 80° C. drying oven.At this point, the precipitate was ground with a mortar and pestle andcalcined in air at 400° C. for 1 hour to remove any remaining moistureand organics.

[0076] BET analysis of the produced powder yielded a surface area of 112m²/g, confirming the presence of nanometer-sized individual particleswith an estimated BET particle size of 11 nm. XRD analyses of allnanoscale powders showed the formation of a single (Ni, Zn)Fe₂O₄ ferritephase with peak shapes characteristic of nanoscale powders. XRD peakbroadening calculations reported an average crystallite size of 20 nm ofthe thermally quenched powders and 8 nm for the chemically derivedpowders. SEM-EDX analyses of sintered nanopowder pellets showed anaverage composition of 14.8% NiO, 15.8% ZnO, and 69.4% Fe₂0₃, whichcorresponded to the targeted stoichiometric composition of theNi_(0.5)ZnO_(0.5) Fe₂O₄.

[0077] Nanoscale ferrite filler powders were uniaxially pressed at 5000pounds in a quarter-inch diameter die set into green pellets. Thepowders were mixed with 2 weight percent Duramax™ binder for improvedsinterability. The amount of powder used for pressing varied from 1.5 to1.7 grams, typically resulting in cylinders having a post-sinteredheight of approximately 1.5 cm. To avoid cracking and other thermalstress effects, a multi-level heating profile was employed. The pelletswere fired at a rate of 5° C./min to 300° C., 1 10° C./min to 600° C.,and 20° C./min to the final sintering temperature where it was held forfour hours. Pellets were cooled from the sintering temperature at a rateof 10 °C./min to ensure the sintering temperature ranged from 900° C. to1300° C., but was typically greater than 1200° C. to ensure anacceptable density. Sintered pellets were then wound with 25 turns of 36gauge enamel coated wire, the wire ends were stripped, and the completedsolenoids where used for electrical characterization. An air coil wasprepared for the purpose of calculating magnetic properties. This coilwas created by winding 25 turns of the enamel coated wire around the dieplunger used previously. This coil was taped with masking tape, slid offthe plunger slowly to maintain shape and characteristics, and wascharacterized along with the ferrite solenoids.

[0078] Inductance characterization was performed with a Hewlett-Packard429A RF Impedance/Materials Analyzer. Impedance, parallel inductance, qfactor, and impedance resistance were measured over a logarithmicfrequency sweep starting at 1 MHz and ending at 1.8 GHz. Values forpermeability (μ) and loss factor (LF) were calculated from inductance(L), air coil inductance (L₀), and impedance resistance (R) using thefollowing equations: $\begin{matrix}{\mu = \frac{L}{L_{0}}} & (3) \\{{LF} = \frac{L_{0}R}{\omega \quad L^{2}}} & (4)\end{matrix}$

[0079] Resistivity measurements were made with a Keithley® 2400SourceMeter using a four-wire probe attachment and TestPoint™ dataacquisition software. Voltage was ramped from 0.1 to 20 volts whilesimultaneously measuring current. The results were plotted as field(voltage divided by pellet thickness) versus current density (currentdivided by electrode cross sectional area). The slope of this graphgives material resistivity (ρ).

[0080] Table 3 summarizes electrical properties of inductors preparedfrom micron-sized powder or from nanopowder. In most cases there is anadvantage to using nanoscale precursor powder instead of micron-sizedpowder. It is important to keep in mind that all measurements were takenfrom cylindrical devices, which have inherently inefficient magneticproperties. Solenoids of this shape were used in this study because ofthe ease of production and excellent reproducibility. All measuredproperties would be expected to improve with the use of higher magneticefficiency shapes such as cores or toroids, or by improving the aspectratio (length divided by diameter) of the cylindrical samples. TABLE 3Micron Nano Micron Nano Loss Factor @ Critical 1 MHz Frequency Average0.0032 0.0025 68.9 78.3 MHz Q Factor @ Resistivity 1 MHz Average 37.252.2 0.84 33.1 MΩ- cm

[0081] The inductors made from ferrite nanopowders exhibitedsignificantly higher Q-factor, critical resonance frequency, andresistivity. They also exhibited more than 20% lower loss factor as isdesired in commercial applications.

[0082] Other embodiments of the invention will be apparent to thoseskilled in the art from a consideration of the specification or practiceof the invention disclosed herein. It is intended that the specificationand examples be considered as exemplary only, with the true scope andspirit of the invention being indicated by the following claims.

What is claimed is:
 1. A nanostructured filler, intimately mixed with amatrix, wherein, the nanostructured filler has a domain sizesufficiently small that a desired material property of the filler variesby a size confinement effect, the desired material property differing byat least 20% from the same property of a powder having the samecomposition as the nanostructured filler and having a domain size of atleast one micron, and the desired material property is selected from thegroup consisting of refractive index, transparency to light, reflectioncharacteristics, resistivity, permittivity, permeability, coercivity,B-H product, magnetic hysteresis, breakdown voltage, skin depth, curietemperature, dissipation factor, loss factor, work function, band gap,electromagnetic shielding effectiveness, radiation hardness,biocompatibility, chemical reactivity, and thermal conductivity.
 2. Ananostructured filler, intimately mixed with a matrix, the filler andmatrix together forming a nanocomposite structure, wherein, thenanostructured filler has a domain size sufficiently small that adesired material property of the nanocomposite differs by at least 20%from the same property of a composite comprising a filler of the samecomposition as the nanostructured filler and having a domain size of atleast one micron, intimately mixed with a matrix of the same compositionas the matrix of the nanocomposite, the proportions of filler and matrixbeing the same for the composite and the nanocomposite, and the desiredmaterial property is selected from the group consisting of refractiveindex, transparency to light, reflection characteristics, resistivity,permittivity, permeability, coercivity, B-H product, magnetichysteresis, breakdown voltage, skin depth, curie temperature,dissipation factor, loss factor, work function, band gap,electromagnetic shielding effectiveness, radiation hardness, chemicalreactivity, thermal conductivity, temperature coefficient of anelectrical property, voltage coefficient of an electrical property,thermal shock resistance, biocompatibility, and wear rate.
 3. Thenanostructured filler of claim 1 or 2, wherein the nanostructured fillercomprises at least one element selected from the group consisting ofactinium, aluminum, arsenic, barium, beryllium, bismuth, cadmium,calcium, cerium, cesium, cobalt, copper, dysprosium, erbium, europium,gadolinium, gallium, gold, hafnium, hydrogen, indium, iridium, iron,lanthanum, lithium, magnesium, manganese, mendelevium, mercury,molybdenum, neodymium, neptunium, nickel, niobium, osmium, palladium,platinum, potassium, praseodymium, promethium, protactinium, rhenium,rubidium, scandium, silver, sodium, strontium, tantalum, terbium,thallium, thorium, tin, titanium, tungsten, vanadium, ytterbium,yttrium, zinc, and zirconium.
 4. The nanostructured filler of claim 3,wherein the nanostructured filler comprises a particle substantiallycomposed of a material selected from the group consisting of ferrites,dielectrics, metals, metal alloys, ceramics, and polymers.
 5. Thenanostructured filler of claim 1 or 2, wherein the nanostructured fillercomprises a particle having a coating.
 6. The nanostructured filler ofclaim 5, wherein the matrix is a polymer and the coating issubstantially composed of a material selected from the group consistingof the polymer and related monomers.
 7. The nanostructured filler ofclaim 5, wherein the coating and the matrix have substantially the samecomposition.
 8. The nanostructured filler of claim 1 or 2, wherein thenanostructured filler has an average domain size of less than or equalto 100 nm.
 9. The nanostructured filler of claim 1 or 2, wherein thenanostructured filler has an average domain size of less than or equalto 50 nm.
 10. The nanostructured filler of claim 1 or 2, wherein thenanostructured filler has an average domain size of less than or equalto 30 nm.
 11. The nanostructured filler of claim 1 or 2, wherein thematrix comprises a polymer.
 12. The nanostructured filler of claim 11,wherein the polymer is selected from the group consisting of poly(methylmethacrylate), poly(vinyl alcohol), polycarbonates, polyalkenes, andpolyaryls.
 13. The nanostructured filler of claim 1 or 2, wherein thematrix comprises a material selected from the group consisting ofceramics, ceramic blends, metals, and metal alloys.
 14. Thenanostructured filler of claim 1 or 2, wherein the nanostructured fillerand the matrix are mixed to form a composite having a volume fraction ofnanostructured filler not greater than 95%.
 15. The nanostructuredfiller of claim 1 or 2, wherein the nanostructured filler and the matrixare mixed to form a composite having a volume fraction of nanostructuredfiller not greater than 80%.
 16. A device comprising the nanostructuredfiller of claim 1 or
 2. 17. The device of claim 16, where the device isselected from the group consisting of electrical devices, magneticdevices, optical devices, biomedical devices, and electrochemicaldevices.
 18. The device of claim 16, where the device is selected fromthe group consisting of varistors, inductors, batteries, medicalimplants, and drug delivery vehicles.
 19. A method of producing acomposite, comprising blending a nanoscale filler composition with anyof a matrix composition and a matrix precursor composition, the fillercomposition comprising no more than 95 volume percent of the composite,wherein, the nanostructured filler has a domain size sufficiently smallthat a desired material property of the nanocomposite differs by atleast 20% from the same property of a composite comprising a filler ofthe same composition as the nanostructured filler, intimately mixed witha matrix of the same composition as the matrix of the nanocomposite, theproportions of filler and matrix being the same for the composite andthe nanocomposite, and the desired material property is selected fromthe group consisting of refractive index, transparency to light,reflection characteristics, resistivity, permittivity, permeability,coercivity, B-H product, magnetic hysteresis, breakdown voltage, skindepth, curie temperature, dissipation factor, work function, band gap,electromagnetic shielding effectiveness, radiation hardness, chemicalreactivity, thermal conductivity, temperature coefficient of anelectrical property, voltage coefficient of an electrical property,thermal shock resistance, biocompatibility, and wear rate.
 20. A methodof producing a composite, comprising blending a nanoscale fillercomposition with any of a matrix composition and a matrix precursorcomposition, the filler composition comprising no more than 95 volumepercent of the composite, wherein, the nanostructured filler has adomain size sufficiently small that a desired material property of thenanocomposite differs by at least 20% from the same property of acomposite comprising a filler of the same composition as thenanostructured filler, intimately mixed with a matrix of the samecomposition as the matrix of the nanocomposite, the proportions offiller and matrix being the same for the composite and thenanocomposite, and the desired material property is selected from thegroup consisting of refractive index, transparency to light, reflectioncharacteristics, resistivity, permittivity, permeability, coercivity,B-H product, magnetic hysteresis, breakdown voltage, skin depth, curietemperature, dissipation factor, work function, band gap,electromagnetic shielding effectiveness, radiation hardness, chemicalreactivity, thermal conductivity, temperature coefficient of anelectrical property, voltage coefficient of an electrical property,thermal shock resistance, biocompatibility, and wear rate.
 21. Themethod of claim 19 or 20, wherein the nanostructured filler comprises atleast one element selected from the group consisting of actinium,aluminum, arsenic, barium, beryllium, bismuth, cadmium, calcium, cerium,cesium, cobalt, copper, dysprosium, erbium, europium, gadolinium,gallium, gold, hafnium, hydrogen, indium, iridium, iron, lanthanum,lithium, magnesium, manganese, mendelevium, mercury, molybdenum,neodymium, neptunium, nickel, niobium, osmium, palladium, platinum,potassium, praseodymium, promethium, protactinium, rhenium, rubidium,scandium, silver, sodium, strontium, tantalum, terbium, thallium,thorium, tin, titanium, tungsten, vanadium, ytterbium, yttrium, zinc,and zirconium.
 22. The method of claim 19 or 20, wherein thenanostructured filler comprises a particle having a coating.
 23. Themethod of claim 19 or 20, wherein the matrix composition comprises amaterial selected from the group consisting of poly(methylmethacrylate), poly(vinyl alcohol), polycarbonate, polyalkenes, andpolyaryls.
 24. The method of claim 19 or 20, wherein the method furthercomprises curing the blended filler and matrix to form a solidcomposite.
 25. The method of claim 19 or 20, wherein the matrixprecursor composition represents a polymer precursor, and wherein themethod further comprises polymerizing the precursor after blending thefiller and the precursor.
 26. The method of claim 19 or 20, wherein thematrix composition is dissolved in a solvent before blending with thefiller, and wherein the solvent is removed after blending with thefiller.
 27. The method of claim 19 or 20, wherein the matrix compositionis substantially in the form of a powder, and the powder is compacted toform a solid composite after blending with the filler.
 28. The method ofclaim 19 or 20, wherein the nanostructured filler has an average domainsize of less than or equal to 100 nm.